1. Field of the Invention
The present invention relates to a closed container for storing an article represented by what is called a photomask that is used in a semiconductor manufacturing process etc, and a management system that can manage a plurality of such closed containers at the same time. More specifically, the present invention relates to what is called a vacuum pod that can maintain more than a certain degree of reduced pressure condition in the article storage space so as to prevent contamination of an article with oxygen, water and particulates that are sometimes called particles, and a container management system that enables checking of the reduced pressure condition in the pod and facilitates maintenance of a prescribed reduced pressure condition.
2. Description of the Related Art
A semiconductor manufacturing process or a process of manufacturing a panel for use in a flat panel display, for example, includes a process of forming minute semiconductor devices etc. such as MOSs and TFTs on a wager or a glass substrate. In this process, a photomask called a reticle is used to form a minute thin film pattern made of a metal, a semiconductor, or an insulator on the substrate. The photomask is composed, for example, of a specific glass substrate and a pattern composed of a thin metal film made of chromium or the like provided on the substrate. The pattern of the thin metal film is precisely transferred by what is called an exposure apparatus onto a photosensitive resist applied on a substrate such as a wafer for making a product. Thereafter, processes including development and etching or milling etc. are performed to produce the above-mentioned minute thin film pattern.
A reticle is used in the pattern transfer process for a number of substrates, and it is required that a reticle be prepared so as to enable transfer of a desired pattern onto resist at any time. Therefore, it is necessary that absorption of oxidizing materials such as oxygen and water that can deteriorate the thin metal film on the reticle and attachment of minute particles that can change the pattern in the exposure process be prevented as much as possible. When a reticle is in use, the exposure apparatus that uses the reticle is in a space in which oxidizing gases and minute particles are controlled very carefully. However, the reticle used needs to be changed in accordance with the product to be manufactured, and it is necessary that a reticle not in use be stored in a specific container for a long time. In addition, it is also necessary that oxidizing gases and minute particles be excluded from the interior of the storage container as much as possible for the above described reason. The storage space in the interior of the container is normally kept in a reduced pressure condition called vacuum, as described in for example Japanese Patent Application Laid-open No. 2004-356478.
If a closed container that does not have its own evacuation system is left after the pressure in the interior thereof is reduced, outside air will enter the interior of the container through seal surfaces between the lid and the body of the container or through a member that constitutes the wall of the container to decrease the degree of vacuum, in ordinary cases. Such a decrease in the degree of vacuum leads to a deterioration of the reticle storage environment. In view of this, it is proper, ideally, that the degree of vacuum in the interior of the container be increased by some operation when the degree of vacuum becomes lower than a prescribed level. However, an apparatus dedicated to improvement of the degree of vacuum in the interior of the container is rarely provided in view of various factors such as the cost and the space for the apparatus. For this reason, in many cases, the container is left in the condition achieved at the time a reticle was placed in the container, and the decrease in the degree of vacuum is left without being taken care of.
When a closed container with a decreased degree of vacuum is set on a semiconductor manufacturing apparatus or the like and the operation of taking out the content article from the interior is performed, the pressure difference between the interior of the closed container and the pressure in the interior of the semiconductor manufacturing apparatus can disturb the pressure in the container and the pressure in the semiconductor manufacturing apparatus, and a problem(s) can arise in the succeeding processing, as has been reported. As a countermeasure to this, Japanese Patent Application Laid-Open No. 2001-274220 discloses a method in which when a closed container is mounted on a semiconductor manufacturing apparatus or the like, the pressure in the interior of the closed container is checked by a system of the apparatus, and the pressure in the interior of the closed container is adjusted by evacuation if necessary. However, according to this method, the pressure etc. in the interior of the closed container cannot be checked unless the container is mounted on the semiconductor manufacturing apparatus or the like. Therefore, conditions such as the pressure in a closed container that is left alone can only be estimated indirectly based on the time elapsed after closing of the container. In other words, it is difficult to appropriately monitor the internal pressure etc. of the closed container in which a content object is stored.